Climate change and changes in weather can affect species in many ways. From altering migration patterns, to varying plant growth leading to deviating diets, to extending or decreasing hibernation periods, climate can ultimately influence the success of a species. In an attempt to study some of these effects, a group of Norwegian scientists have found that extreme climate events can cause population fluctuations not only among single species, but also in a relatively simple high arctic community.

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Scientists, with lead authors from the Centre for Conservation Biology at the Norwegian University of Science and Technology (NTNU), investigated how climate and weather events influenced Arctic populations specifically in Spitsbergen, Svalbard, an arctic island that is home to just four winter species: the wild Svalbard reindeer, the Svalbard rock ptarmigan (a type of bird), the sibling vole, and the arctic fox.

Here, population fluctuations were mainly driven by rain-on-snow events, where rain seeps through the snowpack and pools on top of the frozen soil. It then freezes into an impermeable shell that prevents animals from grazing and reduces food accessibility for populations, causing extensive simultaneous population crashes in all three herbivore species in the following seasons after the extreme weather.

The arctic fox, on the other hand, did not experience population decline mainly due to the abundance of reindeer carcasses, which serves as the foxes' main winter food source. Even though the synchronized die-offs decrease the number of live prey available for foxes to eat, the high number of reindeer carcasses generates a food surplus, which ultimately leads to higher fox reproduction.

However, the reindeer that have survived the extreme weather events will thrive due to the reduced competition for resources and the following winter will have almost no reindeer carcasses. At the same time, the other herbivores that may be a secondary food source for the foxes will not be able to recover after the icing. This results in low fox reproduction and a strong reduction in the arctic fox population size one year after the herbivore die-offs.

"We have known for a long time that climate can synchronize populations of the same species, but these findings suggest that climate and particularly extreme weather events may also synchronize entire communities of species," says lead author Brage Bremset Hansen. "Svalbard's relatively simple ecosystem, which lacks specialist predators, combined with large weather fluctuations from year to year and strong climate signals in the population dynamics of herbivores, are the likely explanations for how such clear climate effects can be observed at the ecosystem level."